columnDefs does not render data

[cooperinho]

I am trying to customize a column data:

    return $this->builder()
        ->setTableId('my-table')
        ->columns($this->getColumns())
        ->dom('frtip')
        ->orderBy(1)
        ->parameters([
            'dom' => 'frtip',
            'width' => "100%",
            'columnDefs' => [
                [
                    'title' => 'My Title',
                    'data' => 'col_three',
                    'target' => [2],                       
                    'searchable' => false,
                    'render' = 'function() { return "Test" + data }' // trying to customize the data displayed in third column
                ]
            ]

this is getColumns():

    protected function getColumns()
    {
        return [
            ['title' => 'Column One', 'data' => 'col_one'],
            ['title' => 'Column Two', 'data' => "col_two"],
            ['data' => 'col_three'],
        ];

I set my columnDefs to be target => [2] which means third column but there is no change in the table